It should probably be said that every atheist should wear a T-shirt that reads "Prove It". That is atheism in a nutshell so to speak.
Now "proving it" is quite difficult yet christians take on this task at times thinking that they will indeed "prove it". Their proof comes in many varied forms, from "look around, the universe seems organized" to testimony.
Now if you follow logic, you'd know that testimony means absolutely nothing without proper corroboration.
Christians like to use biblical testimony as proof and their corroboration is...wait for it...other biblical testimonies. Of course, that isn't corroboration nor is it valid evidence or proof. Another christian proof tactic is the personal testimony. The "I witnessed a miracle" or "god spoke directly to me" crap. The problem is that there is no way to prove that this testimony was not made up and or fabricated.
I know it is frustrating for christians that sane people just don't accept these testimonies as proof, but that is beside the point. In a court of law, a testimony is never accepted as proof alone. Eyewitnesses are notoriously inaccurate, and a testimony could be made up for any number of reasons.
Trump once said that when the Twin Towers were attacked, he saw a bunch of muslims celebrating.
Let's just examine this example.
1) It seems strange and impossible that Trump actually saw anyone from Trump Tower on that day given the dust and debris.
2) Even if he did, he couldn't have seen the people in such detail to actually see if they were or what they were celebrating?
3) How could he tell they were muslim?
There are many other reasons to nullify this testimony.
I used this example to illustrate just how unreliable testimony really is.
So christians, if you think that you can prove a god be advised, testimony is not proof of anything on its own.